In many products, it is extremely important to have an extremely smooth surface in order to permit the product to properly operate. For example, computer hard disks must have a certain flatness within very small limits in order to permit data to be properly stored on the disk. Other devices which require extremely smooth surfaces include optical components, such as lenses and mirrors, silicon wafers and optical discs. In each of these devices, micro-irregularities on the polished surface can spell the difference between an acceptable product and a rejected product. For the above noted devices, irregularities in the order of microns, or millionths of a meter, are critical. To assure proper product quality, the critically smooth products must be tested prior to release to the consumer.